You might want to deactivate your Facebook account in case you want get rid of Facebook temporarily. On the other hand, if you want to leave Facebook forever and do not want to come back, you can delete the account permanently.
Here is how:

1.Turn on your Android phone.

2.Tap the Menu button to go to the apps list.

3.Open your favorite web browser from the given list of apps (E.g. Google Chrome).

4.After opening the web browser, open Facebook website on a new tab.

5.On the opened window, provide your login credentials to sign-in to your Facebook account.6.Once logged-in, type https://www.facebook.com/help/delete_account in the address bar of the web browser.

7.On the displayed page, tap theDelete My Account button under the Delete My Account section.

8.Once done, on thePermanently Delete Accountbox, enter your Facebook password in the Password field.

9.In the Text in the box field, type the captcha code displayed in the image.

10. Finally, tap OK to permanently delete your Facebook account.